The from_array method is shorthand for converting basic forms (and arrays). If you are trying to save something outside of that simple scope, you need to manually look up the objects you want to save.
Simply create an array of DMZ objects, and save those normally. Also, your error is in your controller, it is a PHP error, and it means you are trying to access a property on a non-object. A non-object is any value that isn't an instantiated object, including NULLs.
